The Saudi-led coalition has resumed airstrikes against Shi'ite rebels in Yemen after the end of a five-day humanitarian cease-fire.

The cease-fire expired late Sunday and the coalition airstrikes hit rebel positions in the southern port city of Aden.

Since late March, the coalition has been bombing Iran-backed Houthi rebels in Yemen who had seized Sana'a.

Earlier Sunday, Yemeni political leaders met in the Saudi capital, Riyadh, to discuss a negotiated settlement to the ongoing conflict. No representative of the Houthi rebel group attended. At the same time, fighting continued in a number of flash-points in Yemen.

The conference opened in Riyadh with a traditional Yemeni folk dance, as 400 top political leaders met to discuss the political crisis and military conflict raging in Yemen. But the Houthi rebel group stayed away and demanded talks be held in a neutral country.

Internationally-recognized Yemeni President Abdrabbu Mansour Hadi insisted a U.N. Security Council resolution that calls for the restoration of the country's legitimate government be applied.

He said the Yemeni people await stability, which can only come if the country's legitimate government and its institutions are restored and the Houthi rebels are disarmed. He denounced the group's power-grab last year after a national political power-sharing agreement had been reached.

The Houthis began occupying parts of the capital Sana'a in September. They placed Mr. Hadi under house arrest in February before he fled to Aden. He was then forced to leave the country after Houthi militiamen entered Aden.

Scattered fighting continued in a number of towns and cities Sunday, despite a five-day cease-fire. The Houthis reportedly shelled tribal fighters in parts of Taiz, and clashed with supporters of President Hadi in Ma'arib, Aden, Dalah and Louder. The Houthis claimed the Saudi-led coalition shelled their northern Yemeni stronghold, Saada.

U.N. special envoy for Yemen Ismail Ould Sheikh Ahmed told the gathering in Riyadh that all sides should abide by the conditions of the truce.

He urges all parties present at the conference to allow humanitarian groups to bring aid safely and without hindrance to all parts of the country and not to attack critical infrastructure, such as airports, ports and the road network, in order to make the cease-fire work and to hopefully extend it.

An aid worker at Sana'a Airport told journalists that aid supplies from UNHCR had arrived and would be distributed to the Yemeni people. Other supplies were reported to have arrived in the ports of Aden and Hodeida.